Gasoline sulfur reduction in fluid catalytic cracking

ABSTRACT

The sulfur content of liquid cracking products, especially the cracked gasoline, of the catalytic cracking process is reduced by the use of a sulfur reduction catalyst composition comprising a porous molecular sieve which contains a metal in an oxidation state above zero within the interior of the pore structure of the sieve as well as a cerium component which enhances the stability and sulfur reduction activity of the catalyst. The molecular sieve is normally a faujasite such as USY. The primary sulfur reduction component is normally a metal of Period 3 of the Periodic Table, preferably vanadium. The sulfur reduction catalyst may be used in the form of a separate particle additive or as a component of an integrated cracking/sulfur reduction catalyst.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to application Ser. No. 09/144,607, filed 31Aug. 1998.

This is a continuation of application Ser. No. 09/221,540, filed Dec.28, 1998 now abandoned.

Application Ser. No. 09/221,539, filed concurrently describes catalystcompositions for the reduction of sulfur in gasolines based on largepore zeolites, especially zeolite USY which contain vanadium and rareearth cations.

FIELD OF THE INVENTION

This invention relates to the reduction of sulfur in gasolines and otherpetroleum products produced by the catalytic cracking process. Theinvention provides a catalytic composition for reducing product sulfurand a process for reducing the product sulfur using this composition.

BACKGROUND OF THE INVENTION

Catalytic cracking is a petroleum refining process which is appliedcommercially on a very large scale, especially in the United Stateswhere the majority of the refinery gasoline blending pool is produced bycatalytic cracking, with almost all of this coming from the fluidcatalytic cracking (FCC) process. In the catalytic cracking processheavy hydrocarbon fractions are converted into lighter products byreactions taking place at elevated temperature in the presence of acatalyst, with the majority of the conversion or cracking occurring inthe vapor phase. The feedstock is so converted into gasoline, distillateand other liquid cracking products as well as lighter gaseous crackingproducts of four or less carbon atoms per molecule. The gas partlyconsists of olefins and partly of saturated hydrocarbons.

During the cracking reactions some heavy material, known as coke, isdeposited onto the catalyst. This reduces its catalytic activity andregeneration is desired. After removal of occluded hydrocarbons from thespent cracking catalyst, regeneration is accomplished by burning off thecoke and then the catalyst activity is restored. The threecharacteristic steps of the catalytic cracking can be therefore bedistinguished: a cracking step in which the hydrocarbons are convertedinto lighter products, a stripping step to remove hydrocarbons adsorbedon the catalyst and a regeneration step to burn off coke from thecatalyst. The regenerated catalyst is then reused in the cracking step.

Catalytic cracking feedstocks normally contain sulfur in the form oforganic sulfur compounds such as mercaptans, sulfides and thiophenes.The products of the cracking process correspondingly tend to containsulfur impurities even though about half of the sulfur is converted tohydrogen sulfide during the cracking process, mainly by catalyticdecomposition of non-thiophenic sulfur compounds. The distribution ofsulfur in the cracking products is dependent on a number of factorsincluding feed, catalyst type, additives present, conversion and otheroperating conditions but, in any event a certain proportion of thesulfur tends to enter the light or heavy gasoline fractions and passesover into the product pool. With increasing environmental regulationbeing applied to petroleum products, for example in the ReformulatedGasoline (RFG) regulations, the sulfur content of the products hasgenerally been decreased in response to concerns about the emissions ofsulfur oxides and other sulfur compounds into the air followingcombustion processes.

One approach has been to remove the sulfur from the FCC feed byhydrotreating before cracking is initiated. While highly effective, thisapproach tends to be expensive in terms of the capital cost of theequipment as well as operationally since hydrogen consumption is high.Another approach has been to remove the sulfur from the cracked productsby hydrotreating. Again, while effective, this solution has the drawbackthat valuable product octane may be lost when the high octane olefinsare saturated.

From the economic point of view, it would be desirable to achieve sulfurremoval in the cracking process itself since this would effectivelydesulfurize the major component of the gasoline blending pool withoutadditional treatment. Various catalytic materials have been developedfor the removal of sulfur during the FCC process cycle but, so far, mostdevelopments have centered on the removal of sulfur from the regeneratorstack gases. An early approach developed by Chevron used aluminacompounds as additives to the inventory of cracking catalyst to adsorbsulfur oxides in the FCC regenerator; the adsorbed sulfur compoundswhich entered the process in the feed were released as hydrogen sulfideduring the cracking portion of the cycle and passed to the productrecovery section of the unit where they were removed. See Krishna et al,Additives Improve FCC Process, Hydrocarbon Processing, November 1991,pages 59-66. The sulfur is removed from the stack gases from theregenerator but product sulfur levels are not greatly affected, if atall.

An alternative technology for the removal of sulfur oxides fromregenerator removal is based on the use of magnesium-aluminum spinels asadditives to the circulating catalyst inventory in the FCCU. Under thedesignation DESOX™ used for the additives in this process, thetechnology has achieved a notable commercial success. Exemplary patentson this type of sulfur removal additive include U.S. Pat. Nos.4,963,520; 4,957,892; 4,957,718; 4,790,982 and others. Again, however,product sulfur levels are not greatly reduced.

A catalyst additive for the reduction of sulfur levels in the liquidcracking products is proposed by Wormsbecher and Kim in U.S. Pat. Nos.5,376,608 and 5,525,210, using a cracking catalyst additive of analumina-supported Lewis acid for the production of reduced-sulfurgasoline but this system has not achieved significant commercialsuccess. The need for an effective additive for reducing the sulfurcontent of liquid catalytic cracking products has therefore persisted.

In application Ser. No. 09/144,607, filed 31 Aug. 1998, we havedescribed catalytic materials for use in the catalytic cracking processwhich are capable of reducing the sulfur content of the liquid productsof the cracking process. These sulfur reduction catalysts comprise, inaddition to a porous molecular sieve component, a metal in an oxidationstate above zero within the interior of the pore structure of the sieve.The molecular sieve is in most cases a zeolite and it may be a zeolitehaving characteristics consistent with the large pore zeolites such aszeolite beta or zeolite USY or with the intermediate pore size zeolitessuch as ZSM-5. Non-zeolitic molecular sieves such as MeAPO-5, MeAPSO-5,as well as the mesoporous crystalline materials such as MCM-41 may beused as the sieve component of the catalyst. Metals such as vanadium,zinc, iron, cobalt, and gallium were found to be effective for thereduction of sulfur in the gasoline, with vanadium being the preferredmetal. When used as a separate particle additive catalyst, thesematerials are used in combination with the active catalytic crackingcatalyst (normally a faujasite such as zeolite Y, especially as zeoliteUSY) to process hydrocarbon feedstocks in the fluid catalytic cracking(FCC) unit to produce low-sulfur. Since the sieve component of thesulfur reduction catalyst may itself be an active cracking catalyst, forinstance, zeolite USY, it is also possible to use the sulfur reductioncatalyst in the form of an integrated cracking/sulfur reduction catalystsystem, for example, comprising USY as the active cracking component andthe sieve component of the sulfur reduction system together with addedmatrix material such as silica, clay and the metal, e.g. vanadium, whichprovides the sulfur reduction functionality.

Another consideration in the manufacture of FCC catalysts has beencatalyst stability, especially hydrothermal stability since crackingcatalysts are exposed during use to repeated cycles of reduction (in thecracking step) followed by stripping with steam and then by oxidativeregeneration which produces large amounts of steam from the combustionof the coke, a carbon-rich hydrocarbon, which is deposited on thecatalyst particles during the cracking portion of the cycle. Early inthe development of zeolitic cracking catalysts it was found that a lowsodium content was required not only for optimum cracking activity butalso for stability and that the rare earths such as cerium and lanthanumconferred greater hydrothermal stability. See, for example, FluidCatalytic Cracking with Zeolite Catalysts, Venuto et al., Marcel Dekker,New York, 1979, ISBN 0-8247-6870-1.

SUMMARY OF THE INVENTION

We have now developed catalytic materials for use in the catalyticcracking process which are capable of improving the reduction in thesulfur content of the liquid products of the cracking process including,in particular, the gasoline and middle distillate cracking fractions.The present sulfur reduction catalyst are similar to the ones describedin application Ser. No. 09/144,607 in that a metal component in anoxidation state above zero is present in the pore structure of amolecular sieve component of the catalyst composition, with preferenceagain being given to vanadium. In the present case, however, thecomposition also comprises cerium. We have found that the presence ofthe cerium component not only enhances the stability of the catalyst, ascompared to the catalysts which contain only vanadium or another metalcomponent (other than rare earth) but that it also increases the sulfurreduction activity. This is surprising since cerium in itself has nosulfur reduction activity.

The present sulfur reduction catalysts may be used in the form of anadditive catalyst in combination with the active cracking catalyst inthe cracking unit, that is, in combination with the conventional majorcomponent of the circulating cracking catalyst inventory which isusually a matrixed, zeolite containing catalyst based on a faujasitezeolite, usually zeolite Y. Alternatively, they may be used in the formof an integrated cracking/product sulfur reduction catalyst system.

According to the present invention, the sulfur removal catalystcomposition comprises a porous molecular sieve which contains (i) ametal in an oxidation state above zero within the interior of the porestructure of the sieve and (ii) a cerium component. The molecular sieveis in most cases a zeolite and it may be a zeolite havingcharacteristics consistent with the large pore zeolites such as zeolitebeta or zeolite USY or with the intermediate pore size zeolites such asZSM-5. Non-zeolitic molecular sieves such as MeAPO-5, MeAPSO-5, as wellas the mesoporous crystalline materials such as MCM41 may be used as thesieve component of the catalyst. Metals such as vanadium, zinc, iron,cobalt, and gallium are effective. If the selected sieve material hassufficient cracking activity, it may be used as the active catalyticcracking catalyst component (normally a faujasite such as zeolite Y) or,alternatively, it may be used in addition to the active crackingcomponent, whether or not it has any cracking activity of itself. Thepresent compositions are useful to process hydrocarbon feedstocks influid catalytic cracking (FCC) units to produce low-sulfur gasoline andother liquid products, for example, light cycle oil that can be used asa low sulfur diesel blend component or as heating oil.

While the mechanism by which the metal-containing zeolite catalystcompositions remove the sulfur components normally present in crackedhydrocarbon products is not precisely understood, it does involve theconversion of organic sulfur compounds in the feed to inorganic sulfurso that the process is a true catalytic process. In this process, it isbelieved that a zeolite or other molecular sieve provides shapeselectivity with varying pore size, and the metal sites in zeoliteprovide adsorption sites for the sulfur species.

DETAILED DESCRIPTION

FCC Process

The present sulfur removal catalysts are used as a catalytic componentof the circulating inventory of catalyst in the catalytic crackingprocess, which these days is almost invariably the fluid catalyticcracking (FCC) process. For convenience, the invention will be describedwith reference to the FCC process although the present additives couldbe used in the older moving bed type (TCC) cracking process withappropriate adjustments in particle size to suit the requirements of theprocess. Apart from the addition of the present additive to the catalystinventory and some possible changes in the product recovery section,discussed below, the manner of operating the process will remainunchanged. Thus, conventional FCC catalysts may be used, for example,zeolite based catalysts with a faujasite cracking component as describedin the seminal review by Venuto and Habib, Fluid Catalytic Cracking withZeolite Catalysts, Marcel Dekker, New York 1979, ISBN 0-8247-6870-1 aswell as in numerous other sources such as Sadeghbeigi, Fluid CatalyticCracking Handbook, Gulf Publ. Co. Houston, 1995, ISBN 0-88415-290-1.

Somewhat briefly, the fluid catalytic cracking process in which theheavy hydrocarbon feed containing the organosulfur compounds will becracked to lighter products takes place by contact of the feed in acyclic catalyst recirculation cracking process with a circulatingfluidizable catalytic cracking catalyst inventory consisting ofparticles having a size ranging from about 20 to about 100 microns. Thesignificant steps in the cyclic process are:

(i) the feed is catalytically cracked in a catalytic cracking zone,normally a riser cracking zone, operating at catalytic crackingconditions by contacting feed with a source of hot, regenerated crackingcatalyst to produce an effluent comprising cracked products and spentcatalyst containing coke and strippable hydrocarbons;

(ii) the effluent is discharged and separated, normally in one or morecyclones, into a vapor phase rich in cracked product and a solids richphase comprising the spent catalyst;

(iii) the vapor phase is removed as product and fractionated in the FCCmain column and its associated side columns to form liquid crackingproducts including gasoline,

(iv) the spent catalyst is stripped, usually with steam, to removeoccluded hydrocarbons from the catalyst, after which the strippedcatalyst is oxidatively regenerated to produce hot, regenerated catalystwhich is then recycled to the cracking zone for cracking furtherquantities of feed.

In the present process, the sulfur content of the gasoline portion ofthe liquid cracking products, is effectively brought to lower and moreacceptable levels by carrying out the catalytic cracking in the presenceof the sulfur reduction catalyst.

FCC Cracking Catalyst

The present sulfur reduction catalyst compositions may be used in theform of a separate particle additive which is added to the main crackingcatalyst in the FCCU or, alternatively, they may be used as componentsof the cracking catalyst to provide an integrated cracking/sulfurreduction catalyst system. The cracking component of the catalyst whichis conventionally present to effect the desired cracking reactions andthe production of lower boiling cracking products, is normally based ona faujasite zeolite active cracking component, which is conventionallyzeolite Y in one of its forms such as calcined rare-earth exchanged typeY zeolite (CREY), the preparation of which is disclosed in U.S. Pat. No.3,402,996, ultrastable type Y zeolite (USY) as disclosed in U.S. Pat.No. 3,293,192, as well as various partially exchanged type Y zeolites asdisclosed in U.S. Pat. Nos. 3,607,043 and 3,676,368. Cracking catalystssuch as these are widely available in large quantities from variouscommercial suppliers. The active cracking component is routinelycombined with a matrix material such as silica or alumina as well as aclay in order to provide the desired mechanical characteristics(attrition resistance etc.) as well as activity control for the veryactive zeolite component or components. The particle size of thecracking catalyst is typically in the range of 10 to 100 microns foreffective fluidization. If used as a separate particle additive, thesulfur reduction catalyst (and any other additive) is normally selectedto have a particle size and density comparable to that of the crackingcatalyst so as to prevent component separation during the crackingcycle.

Sulfur Reduction System—Sieve Component

According to the present invention, the sulfur removal catalystcomprises a porous molecular sieve which contains a metal in anoxidation state above zero within the interior of the pore structure ofthe sieve. The molecular sieve is in most cases a zeolite and it may bea zeolite having characteristics consistent with the large pore zeolitessuch as zeolkite Y, preferably zeolite USY, or zeolite beta or with theintermediate pore size zeolites such as ZSM-5, with the former classbeing preferred.

The molecular sieve component of the present sulfur reduction catalystsmay, as noted above, be a zeolite or a non-zeolitic molecular sieve.When used, zeolites may be selected from the large pore size zeolites orintermediate pore zeolites (see Shape Selective Catalysis in IndustrialApplications, Chen et al, Marcel Dekker Inc., New York 1989, ISBN0-8247-7856-1, for a discussion of zeolite classifications by pore sizeaccording to the basic scheme set out by Frilette et al in J. Catalysis67, 218-222 (1981)). The small pore size zeolites such as zeolite A anderionite, besides having insufficient stability for use in the catalyticcracking process, will generally not be preferred because of theirmolecular size exclusion properties which will tend to exclude thecomponents of the cracking feed as well as many components of thecracked products. The pore size of the sieve does not, however, appearto be critical since, as shown below, both medium and large pore sizezeolites have been found to be effective, as have the mesoporouscrystalline materials such as MCM-41.

Zeolites having properties consistent with the existence of a large pore(12 ring) structure which may be used to make the present sulfurreduction catalysts include zeolites Y in its various forms such as Y,REY, CREY, USY, of which the last is preferred, as well as otherzeolites such as zeolite L, zeolite beta, mordenite includingde-aluminated mordenite, and zeolite ZSM-18. Generally, the large poresize zeolites are characterized by a pore structure with a ring openingof at least 0.7 nm and the medium or intermediate pore size zeoliteswill have a pore opening smaller than 0.7 nm but larger than about 0.56nm. Suitable medium pore size zeolites which may be used include thepentasil zeolites such as ZSM-5, ZSM-22, ZSM-23, ZSM-35, ZSM-50, ZSM-57,MCM-22, MCM-49, MCM-56 all of which are known materials. Zeolites may beused with framework metal elements other than aluminum, for example,boron, gallium, iron, chromium.

The use of zeolite USY is particularly desirable since this zeolite istypically used as the active cracking component of the cracking catalystand it is therefore possible to use the sulfur reduction catalyst in theform of an integrated cracking/sulfur reduction catalyst system. The USYzeolite used for the cracking component may also, to advantage, be usedas the sieve component for a separate particle additive catalyst as itwill continue to contribute to the cracking activity of the overallcatalyst present in the unit. Stability is correlated with low unit cellsize with USY and, for optimum results, the UCS for the USY zeolite inthe finished catalyst should be from 2.420 to 2.455 nm, preferably 2.420to 2.445 nm, with the range of 2.435 to 2.440 nm being very suitable.After exposure to the repeated steaming of the FCC cycles, furtherreductions in UCS will take place to a final value which is normallywithin the range of 2.420 to 2.430 nm

In addition to the zeolites, other molecular sieves may be used althoughthey may not be as favorable since it appears that some acidic activity(conventionally measured by the alpha value) is required for optimumperformance. Experimental data indicate that alpha values in excess ofabout 10 (sieve without metal content) are suitable for adequatedesulfurization activity, with alpha values in the range of 0.2 to 2,000being normally suitable¹. Alpha values from 0.2 to 300 represent thenormal range of acidic activity for these materials when used asadditives.

The alpha test is a convenient method of measuring the overall acidity,inclusive of both its internal and external acidity, of a solid materialsuch as a molecular sieve. The test is described in U.S. Pat. No.3,354,078; in the Journal of Catalysis, Vol. 4, p. 527 (1965); Vol. 6,p. 278 (1966); and Vol. 61, p. 395 (1980). Alpha values reported in thisspecification are measured at a constant temperature of 538° C.

Exemplary non-zeolitic sieve materials which may provide suitablesupport components for the metal component of the present sulfurreduction catalysts include silicates (such as the metallosilicates andtitanosilicates) of varying silica-alumina ratios, metalloaluminates(such as germaniumaluminates), metallophosphates, aluminophosphates suchas the silico- and metalloaluminophosphates referred to as metalintegrated aluminophosphates (MeAPO and ELAPO), metal integratedsilicoaluminophosphates (MeAPSO and ELAPSO), silicoaluminophosphates(SAPO), gallogermanates and combinations of these. A discussion on thestructural relationships of SAPO's, AIPO's, MeAPO's, and MeAPSO's may befound in a number of resources including Stud. Surf. Catal. 37 13-27(1987). The AIPO's contain aluminum and phosphorus, whilst in the SAPO'ssome of the phosphorus and/or some of both phosphorus and aluminum isreplaced by silicon. In the MeAPO's various metals are present, such asLi, B, Be, Mg, Ti, Mn, Fe, Co, An, Ga, Ge, and As, in addition toaluminum and phosphorus, whilst the MeAPSO's additionally containsilicon. The negative charge of the Me_(a)Al_(b)P_(c)Si_(d)O_(e) latticeis compensated by cations, where Me is magnesium, manganese, cobalt,iron and/or zinc. Me_(x)APSOs are described in U.S. Pat. No. 4,793,984.SAPO-type sieve materials are described in U.S. Pat. No. 4,440,871;MeAPO type catalysts are described in U.S. Pat. Nos. 4,544,143 and4,567,029; ELAPO catalysts are described in U.S. Pat. No. 4,500,651, andELAPSO catalysts are described in European Patent Application 159,624.Specific molecular sieves are described, for example, in the followingpatents: MgAPSO or MAPSO-U.S. Pat. No. 4,758,419. MnAPSO-U.S. Pat. No.4,686,092; CoAPSO-U.S. Pat. No. 4,744,970; FeAPSO-U.S. Pat. No.4,683,217 and ZnAPSO U.S. Pat. No. 4,935,216. Specificsilicoaluminophosphates which may be used include SAPO-11, SAPO-17,SAPO-34, SAPO-37; other specific sieve materials include MeAPO-5,MeAPSO-5.

Another class of crystalline support materials which may be used is thegroup of mesoporous crystalline materials exemplified by the MCM-41 andMCM-48 materials. These mesoporous crystalline materials are describedin U.S. Pat. Nos. 5,098,684; 5,102,643; and 5,198,203. MCM-41, which isdescribed in U.S. Pat. No. 5,098,684, is characterized by amicrostructure with a uniform, hexagonal arrangement of pores withdiameters of at least about 1.3 nm: after calcination it exhibits anX-ray diffraction pattern with at least one d-spacing greater than about1.8 nm and a hexagonal electron diffraction pattern that can be indexedwith a d100 value greater than about 1.8 nm which corresponds to thed-spacing of the peak in the X-ray diffraction pattern. The preferredcatalytic form of this material is the aluminosilicate although othermetallosilicates may also be utilized. MCM-48 has a cubic structure andmay be made by a similar preparative procedure.

Metal Components

Two metal components are incorporated into the molecular sieve supportmaterial to make up the present catalytic compositions. One component iscerium which is thought to be present in the form of cations within thepore structure of the sieve. The other metal component can be regardedas the primary sulfur reduction component although the manner in whichit effects sulfur reduction is not clear, as discussed in applicationSer. No. 09/144,607, to which reference is made for a description ofsulfur reduction catalyst compositions containing vanadium and othermetal components effective for this purpose. For convenience thiscomponent of the composition will be referred to in this application asthe primary sulfur reduction component. In order to be effective, thismetal (or metals) should be present inside the pore structure of thesieve component. Metal-containing zeolites and other molecular sievescan be prepared by (1) post-addition of metals to the sieve or to acatalyst containing the sieve(s), (2) synthesis of the sieve(s)containing metal atoms in the framework structure, and by (3) synthesisof the sieve(s) with trapped, bulky metal ions in the zeolite pores.Following addition of the metal component, washing to remove unboundionic species and drying and calcination should be performed. Thesetechniques are all known in themselves. Post-addition of the metal ionsis preferred for simplicity and economy, permitting available sievematerials to be converted to use for the present additives. A widevariety of post-addition methods of metals can be used to produce acatalyst of our invention, for example, aqueous exchange of metal ions,solid-state exchange using metal halide salt(s), impregnation with ametal salt solution, and vapor deposition of metals. In each case,however, it is important to carry out the metal(s) addition so that themetal component enters the pore structure of the sieve component.

It has been found that when the metal of the primary sulfur reductioncomponent is present as exchanged cationic species in the pores of thesieve component, the hydrogen transfer activity of the metal componentis reduced to the point that hydrogen transfer reactions taking placeduring the cracking process will normally maintained at an acceptablylow level with the preferred metal components. Thus, coke and light gasmake during cracking increase slightly but they remain within tolerablelimits. Since the unsaturated light ends can be used in any event asalkylation feed and in this way recycled to the gasoline pool, there isno significant loss of gasoline range hydrocarbons incurred by the useof the present additives.

Because of the concern for excessive coke and hydrogen make during thecracking process, the metals for incorporation into the additives shouldnot exhibit hydrogenation activity to a marked degree. For this reason,the noble metals such as platinum and palladium which possess stronghydrogenation-dehydrogenation functionality are not desirable. Basemetals and combinations of base metals with strong hydrogenationfunctionality such as nickel, molybdenum, nickel-tungsten,cobalt-molybdenum and nickel-molybdenum are not desirable for the samereason. The preferred base metals are the metals of Period 3, Groups 5,8, 9, 12, (IUPAC classification, previously Groups 2B, 5B and 8B) of thePeriodic Table. Vanadium, zinc, iron, cobalt, and gallium are effectivewith vanadium being the preferred metal component. It is surprising thatvanadium can be used in this way in an FCC catalyst composition sincevanadium is normally thought to have a very serious effect on zeolitecracking catalysts and much effort has been expended in developingvanadium suppressers. See, for example, Wormsbecher et al, VanadiumPoisoning of Cracking Catalysts: Mechanism of Poisoning and Design ofVanadium Tolerant Catalyst System, J. Catalysis 100, 130-137 (1986). Itis believed that the location of the vanadium inside the pore structureof the sieve immobilizes the vanadium and prevents it from becomingvanadic acid species which can combine deleteriously with the sievecomponent; in any event, the present zeolite-based sulfur reductioncatalysts containing vanadium as the metal component have undergonerepeated cycling between reductive and oxidative/steaming conditionsrepresentative of the FCC cycle while retaining the characteristiczeolite structure, indicating a different environment for the metal.

Vanadium is particularly suitable for gasoline sulfur reduction whensupported on zeolite USY. The yield structure of the V/USY sulfurreduction catalyst is particularly interesting. While other zeolites,after metals addition, demonstrate gasoline sulfur reduction, they tendto convert gasoline to C₃ and C₄ gas. Even though much of the convertedC₃═ and C₄═ can be alkylated and re-blended back to the gasoline pool,the high C₄— wet gas yield may be a concern since many refineries arelimited by their wet gas compressor capacity. The metal-containing USYhas similar yield structure to current FCC catalysts; this advantagewould allow the V/USY zeolite content in a catalyst blend to be adjustedto a target desulfurization level without limitation from FCC unitconstraints. The vanadium on Y zeolite catalyst, with the zeoliterepresented by USY, is therefore a particularly favorable combinationfor gasoline sulfur reduction in FCC. The USY which has been found togive particularly good results is a USY with low unit cell size in therange from 2.420 to 2.450 nm, preferably 2.435 to 2.450 nm (followingtreatment) and a correspondingly low alpha value. Combinations of basemetals such as vanadium/zinc as the primary sulfur reduction componentmay also be favorable in terms of overall sulfur reduction.

The amount of the primary sulfur reduction metal component in the sulfurreduction catalyst is normally from 0.1 to 10 weight percent, typically0.25 to 5 weight percent, (as metal, relative to weight of sievecomponent) but amounts outside this range, for example, up to 10 weightpercent may still be found to give some sulfur removal effect. When thesieve is matrixed, the amount of the primary sulfur reduction metalcomponent expressed relative to the total weight of the catalystcomposition will, for practical purposes of formulation, typicallyextend from 0.05 to 5, more typically from 0.1 to 3 weight percent ofthe entire catalyst.

The second metal component of the sulfur reduction catalyst compositioncomprises cerium which is present within the pore structure of themolecular sieve and is thought to be present in the form of cationsexchanged onto the exchangeable sites present on the sieve component.The cerium component significantly not only improves the catalyststability in the presence of vanadium (or other primary sulfur reductionmetal component) but also enhances the sulfur reduction activity of thecatalyst. For example, higher cracking activity can be achieved with aCe/V/USY catalyst compared to a V/USY catalyst, while comparablegasoline sulfur reduction is obtained. In application Ser. No.09/______, filed concurrently with this application (Mobil IP Case10101-1, PL 98-75), we show that other rare earths are effective forimproving catalyst stability when vanadium is present and thatcombinations of rare earth with cerium are capable of improving sulfurreduction.

The amount of cerium is typically from 0.1 to 10 wt. percent of thecatalyst composition, in most cases from 0.25 to 5 wt. percent. Relativeto the weight of the sieve, the amount of the rare earth will normallybe from about 0.2 to 20 weight percent and in most cases from 0.5 to 10weight percent of the sieve, depending on the sieve:matrix ratio.

The rare earth component can suitably be incorporated into the molecularsieve component by exchange onto the sieve, either in the form of theunmatrixed crystal or of the matrixed catalyst. When the composition isbeing formulated with the preferred USY zeolite sieve, a very effectivemanner of incorporation is to add the rare earth ions to the USY sieve(typically 2.445-2.465 nm unit cell size) followed by additional steamcalcination to lower the unit cell size of the USY to a value typicallyin the range of 2.420 to 2.450, preferably 2.430 to 2.445 nm., afterwhich the primary metal component may be added if not already present.The USY should have a low alkali metal (mainly sodium) content forstability as well as for satisfactory cracking activity; this willnormally be secured by the ammonium exchange made during theultrastabilization process to a desirable low sodium level of not morethan 1 weight percent, preferably not more than 0.5 weight percent, onthe sieve.

The metal components are incorporated into the catalyst composition in away which ensures that they enter the interior pore structure of thesieve. The metals may be incorporated directly into the crystal or intothe matrixed catalyst. When using the preferred USY zeolite as the sievecomponent, this can suitably be done as described above, by recalcininga USY cracking catalyst containing the cerium component to ensure lowunit cell size and then incorporating the metal, e.g. vanadium, by ionexchange or by impregnation under conditions which permit cationexchange to take place so that the metal ion is immobilized in the porestructure of the zeolite. Alternatively, the primary sulfur reductioncomponent and the cerium component can be incorporated into the sievecomponent, e.g. USY zeolite or ZSM-5 crystal, after any necessarycalcination to remove organics from the synthesis after which themetal-containing component can be formulated into the finished catalystcomposition by the addition of the cracking and matrix components andthe formulation spray dried to form the final catalyst.

When the catalyst is being formulated as an integrated catalyst system,it is preferred to use the active cracking component of the catalyst asthe sieve component of the sulfur reduction system, preferably zeoliteUSY, both for simplicity of manufacture but also for retention ofcontrolled cracking properties. It is, however, possible to incorporateanother active cracking sieve material such as zeolite ZSM-5 into anintegrated catalyst system and such systems may be useful when theproperties of the second active sieve material are desired, forinstance, the properties of ZSM-5. The impregnation/exchange processshould in both cases be carried out with a controlled amount of metal sothat the requisite number of sites are left on the sieve to catalyze thecracking reactions which may be desired from the active crackingcomponent or any secondary cracking components which are present, e.g.ZSM-5.

Use of Sulfur Reduction Catalyst Composition

Normally the most convenient manner to use the sulfur reduction catalystwill be as a separate particle additive to the catalyst inventory. Inits preferred form, with zeolite USY as the sieve component, theaddition of the catalyst additive to the total catalyst inventory of theunit will not result in significant reduction in overall crackingbecause of the cracking activity of the USY zeolite. The same is truewhen another active cracking material is used as the sieve component.When used in this way, the composition may be used in the form of thepure sieve crystal, pelleted (without matrix but with added metalcomponents) to the correct size for FCC use. Normally, however, themetal-containing sieve will be matrixed in order to achieve adequateparticle attrition resistance and to maintain satisfactory fluidization.Conventional cracking catalyst matrix materials such as alumina orsilica-alumina, usually with added clay, will be suitable for thispurpose. The amount of matrix relative to the sieve will normally befrom 20:80 to 80:20 by weight. Conventional matrixing techniques may beused.

Use as a separate particle catalyst additive permits the ratio of sulfurreduction and cracking catalyst components to be optimized according tothe amount of sulfur in the feed and the desired degree ofdesulfurization; when used in this manner, it is typically used in anamount from 1 to 50 weight percent of the entire catalyst inventory inthe FCCU; in most cases the amount will be from 5 to 25 weight percent,e.g. 5 to 15 weight percent. About 10 percent represents a norm for mostpractical purposes. The additive may be added in the conventionalmanner, with make-up catalyst to the regenerator or by any otherconvenient method. The additive remains active for sulfur removal forextended periods of time although very high sulfur feeds may result inloss of sulfur removal activity in shorter times.

The alternative to the use of the separate particle additive is to usethe sulfur reduction catalyst incorporated into the cracking catalyst toform an integrated FCC cracking/gasoline sulfur reduction catalyst. Ifthe sulfur reduction metal components are used in combination with asieve other than the active cracking component, for example, on ZSM-5 orzeolite beta, when the main active cracking component is USY, the amountof the sulfur reduction components (sieve plus metals) will typically beup to 25 weight percent of the entire catalyst or less, corresponding tothe amounts in which it may be used as a separate particle additive, asdescribed above.

Other catalytically active components may be present in the circulatinginventory of catalytic material in addition to the cracking catalyst andthe sulfur removal additive. Examples of such other materials includethe octane enhancing catalysts based on zeolite ZSM-5, CO combustionpromoters based on a supported noble metal such as platinum, stack gasdesulfurization additives such as DESOX™ (magnesium aluminum spinel),vanadium traps and bottom cracking additives, such as those described inKrishna, Sadeghbeigi, op cit. and Scherzer, Octane Enhancing ZeoliticFCC Catalysts, Marcel Dekker, New York, 1990, ISBN 0-8247-8399-9. Theseother components may be used in their conventional amounts.

The effect of the present additives is to reduce the sulfur content ofthe liquid cracking products, especially the light and heavy gasolinefractions although reductions are also noted in the light cycle oil,making this more suitable for use as a diesel or home heating oil blendcomponent. The sulfur removed by the use of the catalyst is converted toinorganic form and released as hydrogen sulfide which can be recoveredin the normal way in the product recovery section of the FCCU in thesame way as the hydrogen sulfide conventionally released in the crackingprocess. The increased load of hydrogen sulfide may impose additionalsour gas/water treatment requirements but with the significantreductions in gasoline sulfur achieved, these are not likely to beconsidered limitative.

Very significant reductions in gasoline sulfur can be achieved by theuse of the present catalysts, in some cases up to about 60% relative tothe base case using a conventional cracking catalyst, at constantconversion, using the preferred form of the catalyst described above.Gasoline sulfur reduction of 25% is readily achievable with many of theadditives according to the invention, as shown by the Examples below.The extent of sulfur reduction may depend on the original organic sulfurcontent of the cracking feed, with the greatest reductions achieved withthe higher sulfur feeds. The metals content of the equilibrium catalystin the unit may also affect the degree of desulfurization achieved, witha low metals content, especially vanadium content, on the equilibriumcatalyst favoring greater desulfurization. Desulfurization will be veryeffective with E-catalyst vanadium contents below 1,000 ppm although thepresent catalyst remain effective even at much higher vanadium contents.Sulfur reduction may be effective not only to improve product qualitybut also to increase product yield in cases where the refinery crackedgasoline end point has been limited by the sulfur content of the heavygasoline fraction; by providing an effective and economical way toreduce the sulfur content of the heavy gasoline fraction, the gasolineend point may be extended without the need to resort to expensivehydrotreating, with a consequent favorable effect on refinery economics.Removal of the various thiophene derivatives which are refractory toremoval by hydrotreating under less severe conditions is also desirableif subsequent hydrotreatment is contemplated.

EXAMPLE 1

Preparation of Catalyst Series I

A V/USY catalyst, Catalyst A, was prepared using a commercial H-form USY(crystal) with a bulk silica-to-alumina ratio of 5.4 and 2.435 nm unitcell size. A fluid catalyst was prepared by spray drying aqueous slurrycontaining 40 wt % of the USY crystals, 25 wt % silica, 5 wt % alumina,and 30 wt % kaolin clay. The spray-dried catalyst was calcined at 540°C. (1000° F.) for 3 hours. The resulting H-form USY catalyst wasimpregnated with a vanadium oxalate solution to target 0.4 wt % V byincipient wetness impregnation. The impregnated V/USY catalyst wasfurther air calcined at 540° C. (1000° F.) for 3 hours. The finalcatalyst contains 0.39% V.

A Ce+V/USY catalyst, Catalyst B, was prepared from the same, spray-driedH-form USY catalyst intermediate as Catalyst A. The H-form USY catalystwas impregnated with a solution of Ce(NO₃)₃ to target 1.5 wt % Celoading using an incipient wetness impregnation method. Resulting Ce/USYcatalyst was air calcined at 540° C. (1000° F.) for 3 hours followed bysteaming at 540° C. (1000° F.) for 3 hours. Then the catalyst wasimpregnated with a vanadium oxalate solution to target 0.4 wt % V byincipient wetness impregnation. The impregnated Ce+V/USY catalyst wasfurther air calcined at 540° C. (1000° F.) for 3 hours. The finalcatalyst contains 1.4% Ce and 0.43% V.

TABLE 1 Physical Properties of the V and Ce+V USY/ Silica-Alumina-ClayCatalysts V/USY Ce+V/USY Catalyst A Catalyst B Calcined Cat. V loading,wt % 0.39 0.43 Ce loading, wt % N.A. 1.4 Surface area, m²g⁻¹ 302 250Alpha 130 12 UCS, nm 2.436 2.437

EXAMPLE 2

Preparation of Catalyst Series 2

All samples in Catalyst Series 2 were prepared from a single source ofspray dried material, consisting of 50% USY, 21% silica sol and 29%clay. The starting USY had a bulk silica-to-alumina ratio of 5.4 and2.435 nm unit cell size. The spray dried catalyst was slurried with asolution of (NH₄)₂SO₄ and NH₄OH at pH of 6 to remove Na⁺, followed bywashing with water and air calcination at 650° C. (1200° F.) for 2hours.

A V/USY catalyst, Catalyst C, was prepared using the above H-form USYcatalyst. The H-form USY catalyst was impregnated with a vanadiumoxalate solution to target 0.5 wt % V by incipient wetness impregnation.The impregnated V/USY catalyst was further air calcined at 650° C.(1200° F.) for 2 hours. The final catalyst contains 0.53% V.

A Ce+V/USY catalyst, Catalyst D, was prepared from the above H-form USYcatalyst. The H-form USY catalyst was exchanged with a solution of CeCl₃to target 0.75 wt % Ce loading. Resulting Ce/USY catalyst was aircalcined and impregnated with a vanadium oxalate solution to target 0.5wt % V by incipient wetness impregnation. The impregnated Ce+V/USYcatalyst was further air calcined. The final catalyst contains 0.72% Ceand 0.52% V.

A Ce+V/USY catalyst, Catalyst E, was prepared from the above H-form USYcatalyst by an exchange with a solution of CeCl₃ to target 3 wt % Celoading. Resulting Ce/USY catalyst was air calcined and impregnated witha vanadium oxalate solution to target 0.5 wt % V by incipient wetnessimpregnation. The impregnated Ce+V/USY catalyst was further aircalcined. The final catalyst contains 1.5% Ce and 0.53% V.

A Ce+V/USY catalyst, Catalyst F, was prepared from the above H-form USYcatalyst by an incipient wetness impregnation with a solution of CeCl₃to target 1.5 wt % Ce loading. Resulting Ce/USY catalyst was aircalcined and impregnated with a vanadium oxalate solution to target 0.5wt % V by incipient wetness impregnation. The impregnated Ce+V/USYcatalyst was further air calcined. The final catalyst contains 1.5% Ceand 0.53% V.

These catalysts were then steamed deactivated, to simulate catalystdeactivation in an FCC unit, in a fluidized bed steamer at 770° C.(1420° F.) for 20 hours using 50% steam and 50% gas. The gas stream waschanged from air, N₂, propylene, and to N₂ for every ten minutes, thencircled back air to simulate the coking/regeneration cycle of a FCC unit(cyclic steaming). Two samples of deactivated catalysts were generated:the steam deactivation cycle was ended with air-burn (ending-oxidation)for one batch of catalysts, and the other ended with propylene(ending-reduction). The coke content of the “ending-reduction” catalystis less than 0.05% C. The physical properties of the calcined and steamdeactivated catalysts are summarized in Table 2.

TABLE 2 Physical Properties of V and Ce+V USY/Silica Sol Catalysts V/USYCe+V/USY Ce+V/USY Ce+V/USY Catalyst C Catalyst D Catalyst E Catalyst FCalcined Cat. V loading, wt % 0.53 0.52 0.53 0.53 Ce loading, wt % N.A.0.72 1.5 1.5 Na, ppm 890 1190 1190 1260 Deactivated Cat. (CPS 770° C.,20 hrs) Surface area, 237 216 208 204 m²g⁻¹ Unit cell size, nm 2.4252.423 2.425 2.425

EXAMPLE 3

Preparation of Catalyst Series 3

All samples in Catalyst Series 3 were prepared from a single source ofspray dried material, consisting of 40% USY, 30% colloidal silica sol,and 30% clay. The starting H-form USY had a bulk silica-to-alumina ratioof 5.4 and 2.435 nm unit cell size. The spray-dried catalyst was aircalcined at 540° C. (1000° F.) for 3 hours.

A Ce/USY catalyst, Catalyst G, was prepared using the above H-form USYcatalyst. The H-form USY catalyst was impregnated with a solution ofCe(NO₃)₃ to target 1.5 wt % Ce loading using an incipient wetnessimpregnation method. Resulting Ce/USY catalyst was air calcined at 540°C. (1000° F.) followed by steaming at 540° C. (1000° F.) for 3 hours.

A Ce+V/USY catalyst, Catalyst H, was prepared from Catalyst G. TheCe/USY catalyst was impregnated with a vanadium oxalate solution totarget 0.5 wt % V by incipient wetness impregnation. The impregnatedCe+V/USY catalyst was dried and air calcined at 540° C. (1000° F.) for 3hours. The final catalyst contains 1.4% Ce and 0.49% V.

A Ce+V/USY catalyst, Catalyst I, was prepared from Catalyst G by anexchange with a solution of VOSO4 at pH ˜3 to target 0.5 wt % V loading.Resulting Ce+V/USY catalyst was dried and air calcined at 540° C. (1000°F.) for 3 hours. The final catalyst contains 0.9% Ce and 0.47% V.Physical properties of calcined catalysts are summarized in Table 3.

TABLE 3 Physical Properties of the Ce and Ce+V USY/Silica-Clay CatalystsCe/USY Ce+V/USY Ce+V/USY Catalyst G Catalyst H Catalyst I Calcined Cat.V loading, wt % N.A. 0.49 0.47 Ce loading, wt % 1.6 1.4 0.9 Na, ppm — —940 Surface area, m²g⁻¹ 284 281 272 Alpha — 10 14 Unit cell size, nm2.435 2.436 2.436

EXAMPLE 4

Fluid Catalytic Cracking Evaluation of Series 1 Catalysts

The V and Ce+V USY catalysts from Example 1 were steam deactivated in afluidized bed steamer at 770° C. (1420° F.) for 20 hours using 50% steamand 50% gas. The gas stream was changed from air, N₂, propylene, and toN₂ for every ten minutes, then circled back air to simulatecoking/regeneration cycle of a FCC unit (cyclic steaming). The steamdeactivation cycle was ended with air-burn (ending-oxidation).Twenty-five weight percent of steamed additive catalysts were blendedwith an equilibrium catalyst from an FCC unit. The equilibrium catalysthas very low metals level (120 ppm V and 60 ppm Ni).

The blended catalysts were tested for gas oil cracking activity andselectivity using an ASTM microactivity test (ASTM procedure D-3907).The vacuum gas oil feed stock properties are shown in Table 4 below. Arange of conversions was scanned by varying the catalyst-to-oil ratiosand reactions were run at 527° C. (980° F.). Gasoline range product fromeach material balance was analyzed with a sulfur GC (AED) to determinethe gasoline S concentration. To reduce experimental errors in Sconcentration associated with fluctuations in distillation cut point ofgasoline, we quantitated S species ranging from thiophene toC₄-thiophenes in syncrude (excluding benzothiophene and higher boiling Sspecies) and the sum was defined as “cut-gasoline S.”

TABLE 4 Properties of Vacuum Gas Oil Feed Charge Stock Properties VacuumGas Oil API Gravity 26.6 Aniline Point, ° C. 83 CCR, wt % 0.23 Sulfur,wt % 1.05 Nitrogen, ppm 600 Basic nitrogen, ppm 310 Ni, ppm 0.32 V, ppm0.68 Fe, ppm 9.15 Cu, ppm 0.05 Na, ppm 2.93 Distillation, ° C. IBP, oF181 50 wt %, 380 99.5%, 610

Performances of the catalysts are summarized in Table 5, where theproduct selectivity was interpolated to a constant conversion, 7 wt %conversion of feed to 220° C.−(430° F.−) material.

TABLE 5 Catalytic Cracking Performance of Series 1 Catalysts ECat +25%V/USY cat +25% Ce+V/USY Base Case (Catalyst A) cat (Catalyst B) MATProduct Yields Conversion, wt % 70 70 70 Cat/Oil 3.3 3.8 3.7 H2 yield,wt % 0.03 +0.04 +0.13 C1 + C2 Gas, wt % 1.4 +0.1 +0.1 Total C3 Gas, wt %5.4 +0.1 −0.1 C3 = yield, wt % 4.5 +0.1 −0.1 Total C4 Gas, wt % 10.9+0.2 −0.2 C4 = yield, wt % 5.2 +0.4 +0.2 iC4 yield, wt % 4.8 −0.2 −0.4C5 + Gasoline, wt % 48.9 −0.3 −0.3 LFO, wt % 24.6 +0.5 +0.3 HFO, wt %4.7 −0.2 −0.1 Coke, wt % 2.7 +0 +0.5 Cut Gasoline S, PPM 529 378 235 %Reduction in Cut Base 29 56 Gasoline S

Table 5 compares the FCC performances of V/USY andCe+V/USY/Silica-Alumina-Clay catalysts each blended with an equilibriumFCC catalyst (ECat).

Compared to the ECat base case, the addition of V/USY and Ce+V/USYcatalyst changes the overall product yield structure only slightly.Yield changes in C4- gas, gasoline, light cycle oil, and heavy fuel oilare all small. Moderate increases in hydrogen and coke yields wereobserved. While the product yield changes were small, the V/USY andCe+V/USY catalysts changed the gasoline S concentration substantially.When 25 wt % of Catalyst A (10 wt % V/USY zeolite addition, referencecatalyst) was blended with an equilibrium FCC catalyst, 29% reduction ingasoline sulfur concentration was achieved. In comparison, Ce+V/USYcatalyst (Catalyst B) gave 56% reduction in gasoline S. Addition of Ceto the V/USY catalyst reduced the gasoline S content by additional 27%,i.e., 93% improvement over the V/USY reference catalyst. Both catalystshave comparable vanadium loadings (0.39% vs. 0.43% V). In light of thefact that Ce by itself does not have any gasoline sulfur reductionactivity (see below in Example 7), these results are quite unexpectedand dearly demonstrate the benefits of cerium addition.

EXAMPLE 5

Fluid Catalytic Cracking Evaluation of Series 2 Catalysts After CyclicSteaming

The performances of V and Ce+V catalysts from Example 2 are summarizedin this example. The Series 2 catalysts were steam deactivated asdescribed above by cyclic steaming (ending-reduction), then blended withan equilibrium catalyst from an FCC unit in a 25:75 weight ratio. Theequilibrium catalyst has very low metals level (120 ppm V and 60 ppmNi). The results are summarized in Table 6.

TABLE 6 Catalytic Cracking Performance of V vs. Ce+V/USY/ Silica-SolCatalysts ECat +25% +25% +25% Base V/USY cat Ce+V/USY Ce+V/USY Case (CatC) (Cat E) (Cat F) MAT Product Yields Conversion, wt % 65 65 65 65Cat/Oil 3.0 3.4 3.2 3.3 H2 yield, wt % 0.03 +0.02 +0.02 +0.02 C1 + C2Gas, wt % 1.1 +0 +0 +0.1 Total C3 Gas, wt % 4.4 −0.1 −0.1 +0 C3 = yield,wt % 3.7 +0 −0.1 +0 Total C4 Gas, wt % 9.5 −0.1 −0.2 −0.1 C4 = yield, wt% 4.8 +0.1 +0.1 +0.1 iC4 yield, wt % 4.1 −0.2 −0.3 −0.1 C5 + Gasoline,wt % 47.4 +0.1 +0.5 +0.1 LFO, wt % 29.7 −0.2 +0 −0.1 HFO, wt % 5.3 +0.2+0 +0.1 Coke, wt % 2.3 +0.1 −0.1 +0 Cut Gasoline S, PPM 516 489 426 426% Reduction in Cut Base 5.2 17.4 17.4 Gasoline S

Table 6 compares FCC performances of V/USY and Ce+V/USY/Silica-Soladditive catalysts after cyclic steam deactivation (ending-reduction).

The deactivated additive catalysts were each blended with an equilibriumFCC catalyst. Compared to the ECat base case, addition of the V/USY andCe+V/USY catalysts made very little changes in the overall product yieldstructure. The yields of hydrogen, C4- gas, gasoline, light cycle oil,heavy fuel oil and coke were changed by less than 0.2 wt % each.Additions of the V/USY and Ce+V/USY catalysts changed the gasoline Sconcentration to different extents. When 25 wt % of Catalyst C(V/USY—reference catalyst) was blended with the equilibrium FCCcatalyst, 5.2% reduction in gasoline sulfur concentration was achieved.For comparison, Ce+V/USY catalysts (Catalysts E and F) gave 17.4%reduction in gasoline S, respectively. Addition of Ce to the V/USYcatalyst reduced the gasoline S content by additional 12.3%, i.e., 237%improvement over the V/USY reference catalyst.

EXAMPLE 6

Fluid Catalytic Cracking Evaluation of Series 2 Catalysts After CyclicSteaming

The performances of the V and Ce+V catalysts from Example 2 after cyclicsteam deactivation are summarized in this example. The catalysts ofExample 2 were deactivated by cyclic steaming as described above(ending-oxidation) and were then blended with an equilibrium catalystfrom an FCC unit in 25:75 weight ratio. The equilibrium catalyst hasvery low metals level (120 ppm V and 60 ppm Ni). The results aresummarized in Table 7.

TABLE 7 Catalytic Cracking Performance of V vs. Ce+V/USY/ Silica-SolCatalyst ECat +25% +25% +25% Base V/USY cat Ce+V/USY Ce+V/USY Case (CatC) (Cat D) (Cat E) MAT Product Yields Conversion, wt % 70 70 70 70Cat/Oil 2.8 3.7 3.6 3.4 H2 yield, wt % 0.03 +0.12 +0.13 +0.12 C1 + C2Gas, wt % 1.5 +0.2 +0.2 +0.1 Total C3 Gas, wt % 5.5 +0.1 +0 −0.1 C3 =yield, wt % 4.7 +0 +0 −0.1 Total C4 Gas, wt % 11.1 +0 +0 −0.2 C4 =yield, wt % 5.8 +0.1 +0.1 +0 iC4 yield, wt % 4.6 −0.1 −0.2 −0.2 C5 +Gasoline, wt % 49.4 −1.0 −0.9 −0.5 LFO, wt % 25.6 −0.1 +0 +0.2 HFO, wt %4.4 +0.1 +0 −0.2 Coke, wt % 2.3 +0.6 +0.5 +0.5 Cut Gasoline S, PPM 579283 243 224 % Reduction in Cut Base 51.1 58.1 61.3 Gasoline S

Table 7 compares the FCC performances of V/USY and Ce+V/USY/Silica-Soladditive catalysts after cyclic steam deactivation (ending-oxidation).

Compared to the ECat base case, addition of V/USY and Ce+V/USY catalystmade slight changes in the overall product yield structure. There weremoderate increases in hydrogen and coke yields. Also a small changes inC4- gas yield gasoline, light cycle oil and heavy fuel oil wereobserved. Addition of the V/USY and Ce+V/USY catalysts changed thegasoline S concentration substantially. When 25 wt % of Catalyst C(V/USY—reference catalyst) was blended with an equilibrium FCC catalyst,51.1% reduction in gasoline sulfur concentration was achieved. Incomparison, the Ce+V/USY catalysts (Catalysts D and E) gave 58.1% and61.3% reduction in gasoline S, respectively. Addition of Ce to the V/USYcatalyst reduced the gasoline S content by additional 7.0-10.2%, i.e.,up to 20% improvement over the V/USY reference catalyst.

The product yields data of the V/USY and Ce+V/USY catalysts indicatethat the yield changes from the ECat is due to addition of vanadium tothe USY catalyst The product yields of V/USY catalyst is comparable tothose of Ce+V/USY catalysts except the gasoline S level. These resultssuggest that Ce increases the gasoline sulfur reduction activity of theV/USY additive catalyst with little effect on product yields.

EXAMPLE 7

Fluid Catalytic Cracking Evaluation of Series 3 Catalysts, Study ofPromotional Effects

Performances of the Ce and Ce+V catalysts from Example 3 after cyclicsteaming deactivation (ending-reduction) as described above, aresummarized in this example. The deactivated catalysts were blended withan equilibrium catalyst from an FCC unit in 25:75 weight ratio. Theequilibrium catalyst has very low metals level (120 ppm V and 60 ppmNi). The results are summarized in Table 8.

TABLE 8 Catalytic Cracking Performance of Ce vs. Ce+V/USY/ Silica-ClayCatalysts ECat +25% +25% +25% Base Ce/USY Ce+V/USY Ce+V/USY Case (Cat G)(Cat H) (Cat I) MAT Product Yields Conversion, wt % 70 70 70 70 Cat/Oil3.2 3.4 3.7 3.9 H2 yield, wt % 0.04 +0 +0.07 +0.07 C1 + C2 Gas, wt % 1.5+0.1 +0.1 +0.1 Total C3 Gas, wt % 5.7 +0.1 −0.1 +0 C3 = yield, wt % 4.8+0 +0 +0 Total C4 Gas, wt % 11.5 +0 −0.3 −0.1 C4 = yield, wt % 5.7 +0+0.1 +0.1 iC4 yield, wt % 4.9 +0 −0.3 −0.2 C5 + Gasoline, wt % 48.8 −0.2−0.2 −0.7 LFO, wt % 25.5 +0 +0.1 +0.1 HFO, wt % 4.5 +0 −0.1 −0.1 Coke,wt % 2.4 +0 +0.3 +0.6 Cut Gasoline S, PPM 486 487 341 351 % Reduction inCut Base 0 29.8 27.7 Gasoline S

Table 8 compares FCC performances of Ce/USY and Ce+V/USY/Silica-clayadditive catalysts after cyclic steam deactivation (ending-reduction).

Compared to the ECat base case, addition of the Ce/USY catalyst madealmost no changes in overall product yields. Addition of the Ce+V/USYcatalyst made slight changes in the overall product yield structure.There were moderate increases in hydrogen and coke yields, as well asslight changes in C4-gas, gasoline, light cycle oil and heavy fuel oilyields. Addition of the Ce/USY catalysts made a no change in thegasoline S concentration. In contrast, Ce+V/USY catalysts (Catalysts Hand I, invention) gave 29.8% and 27.7% reduction in gasoline S,respectively. These results indicate that cerium by itself does not haveany gasoline sulfur reduction activity. Cerium appears to have apromotional effect for vanadium to increase the activity of a V/USYgasoline sulfur reduction additive catalyst

1. A method of reducing the sulfur content of a liquid catalyticallycracked petroleum fraction, which comprises catalytically cracking apetroleum feed fraction containing organosulfur compounds at elevatedtemperature in the presence of an equilibrium cracking catalyst and aproduct sulfur reduction catalyst which comprises a porous molecularsieve having (i) a first metal component which is within the interiorpore structure of the molecular sieve and which comprises vanadium in anoxidation state greater than zero and (ii) a second metal componentcomprising cerium which is within the interior pore structure of themolecular sieve, to produce liquid cracking products of reduced sulfurcontent.
 2. A method according to claim 1 in which the product sulfurreduction catalyst comprises a large pore size or intermediate pore sizezeolite as the molecular sieve component.
 3. A method according to claim2 in which the large pore size zeolite comprises a faujasite zeolite. 4.A method according to claim 2 in which the large pore size zeolitecomprises zeolite USY.
 5. A method according to claim 1 in which thesecond metal component is present in an amount from 0.5 to 10 weightpercent of the catalytic composition.
 6. A method according to claim 1in which the product sulfur reduction catalyst comprises a USY zeolitehaving a UCS of from 2.420 to 2.455 nm; and a bulk silica:alumina ratioof at least 5.0 as the molecular sieve component.
 7. A method accordingto claim 1 in which the sulfur reduction catalyst is a separate particleadditive catalyst.
 8. In a fluid catalytic cracking process in which aheavy hydrocarbon feed comprising organosulfur compounds iscatalytically cracked to lighter products by contact in a cycliccatalyst recirculation cracking process with a circulating fluidizablecatalytic cracking catalyst inventory consisting of particles having asize ranging from about 20 to about 100 microns, comprising: (i)catalytically cracking the feed in a catalytic cracking zone operatingat catalytic cracking conditions by contacting feed with a source of anequilibrium cracking catalyst to produce a cracking zone effluentcomprising cracked products and spent catalyst containing coke andstrippable hydrocarbons; (ii) discharging and separating the effluentmixture into a cracked product rich vapor phase and a solids rich phasecomprising spent catalyst; (iii) removing the vapor phase as a productand fractionating the vapor to form liquid cracking products includinggasoline; (iv) stripping the solids rich spent catalyst phase to removeoccluded hydrocarbons from the catalyst; (v) transporting strippedcatalyst from the stripper to a catalyst regenerator; (vi) regeneratingstripped catalyst by contact with oxygen containing gas to produceregenerated catalyst; and (vii) recycling the regenerated catalyst tothe cracking zone to contact further quantities of heavy hydrocarbonfeed, the improvement which comprises reducing the sulfur content of thegasoline portion of the liquid cracking products, by catalyticallycracking the feed fraction at elevated temperature in the presence of aproduct sulfur reduction catalyst which comprises a porous molecularsieve having (i) vanadium which is within the interior, pore structureof the molecular sieve and which is in an oxidation state greater thanzero and (ii) a second metal component which is within the interior porestructure of the molecular sieve and which comprises cerium.
 9. A methodaccording to claim 8 in which the cracking catalyst comprises a matrixedfaujasite zeolite.
 10. A method according to claim 8 in which theproduct sulfur reduction catalyst comprises a large pore size orintermediate pore size zeolite as the molecular sieve component andcerium as the second metal component.
 11. A method according to claim 10in which the large pore size zeolite of the product sulfur reductioncatalyst comprises zeolite USY.